Regarding data transmission, there is a conventional ATM method wherein all data to be sent are divided into 53-byte ATM cell units which are then sent/received at high speed. Specifically, data to be sent (user information) is stored in the payload of the exchange unit in the ATM cell, and destination information and the like on the send destination of data are stored in the header of the ATM cells, followed by transmission using preset ATM connection to perform data communication.
In this case, for example, a virtual path identifier/virtual channel identifier (VPI/VCI) is used as the destination information, and, according to these identifiers, the ATM cells are transmitted through a predetermined ATM line within an ATM network.
FIG. 1 is a conceptual diagram showing the construction of a conventional ATM cell communication system. As shown in FIG. 1, the conventional ATM cell communication system comprises: a plurality of terminals, such as personal computers; ATM communication apparatuses 1, 3 provided respectively with adaptors 4, 5 for ATM cells (hereinafter referred to as “cells”) multiplexing or demultiplexing; ATM exchanges 6, 7 for performing switching between the plurality of terminals and the ATM communication apparatuses 1, 3; and an ATM network 2 composed of a virtual path for connecting the ATM communication apparatuses 1, 3 to each other
For example, as soon as cells are output from any terminal connected to the ATM exchange 6, the cells are input through the ATM exchange 6 into the ATM communication apparatus 1. In the ATM communication apparatus 1, the received cells are multiplexed in the adaptor 4, followed by send to the ATM communication apparatus 3 side through the ATM network 2 composed of a virtual path. In the ATM communication apparatus 3, the received multiplexed cells are separated, and the separated cells are input into the ATM exchange 7. The ATM exchange 7 sends the received cells to the send destination terminal.
Here the virtual path is a path between end points, which enable a large quantity of simultaneous connections, and a plurality of virtual channels are defined in the virtual path. In this connection, it should be noted that, for communication entrepreneurs for providing ATM lines, it is common practice to set an accounting system which depends upon the number of virtual channels. This means that the usage charge for the ATM line increases with increasing the number of contract virtual channels.
Accordingly, in order to reduce the usage charge for the ATM lines, the contract virtual channel has been changed to a virtual channel having a higher data transfer rate, and a plurality of virtual channels are multiplexed in the virtual path to reduce the number of contract virtual channels.
In order to reduce the number of contract virtual channels through multiplexing of a plurality of virtual channels within the virtual path, however, processing for the change is necessary on the ATM cell communication apparatus side, and this process requires the cost of equipment. That is, the conventional method cannot reduce the usage charge for the ATM lines,